Nebulizers used in medical applications typically entrain a medical liquid or water into a high-velocity flow of pressurized carrier gas, such as oxygen, in order to atomize the liquid into a fine mist or aerosol within the carrier gas. The atomized liquid is entrained and carried in the gas stream through a delivery tube to a patient some distance away for inhalation.
Currently available nebulizers include a housing with a carrier gas input nozzle, a reservoir opening and an output opening. A relatively high velocity flow of carrier gas enters the housing through the carrier gas input nozzle. A reservoir port is located within the housing at the output side of the nozzle, the flow of carrier gas being directed across and slightly towards the reservoir port. Notwithstanding the slightly increased "back pressure" within the enclosure that this non-linear carrier gas flow creates, considerable liquid is still drawn into the flow of carrier gas through the reservoir port by virtue of the relatively low pressure created within the housing by the high velocity flow of carrier gas. The liquid is subsequently atomized into a fine mist and the entrained atomized liquid is carried in the carrier gas stream to the patient.
An additional feature found on many currently available nebulizers is an adjustable air inlet opening in the housing adjacent the carrier gas input nozzle. This opening allows air to be drawn into the housing to be mixed with the carrier gas stream in addition to the liquid to reduce the concentration of carrier gas in the resultant mixture. As the most commonly used carrier gas in medical nebulizers is oxygen and since many patients, such as those suffering from emphysema, cannot or need not be exposed to high concentrations of oxygen, this feature often eliminates a need to initially dilute the oxygen carrier gas with pressurized air. As a result, complicated air pressurizing and mixing apparatus need not be used.
While nebulizers have improved significantly over the years, several significant drawbacks still exist with current nebulizer designs. For example, patients with emphysema are quite sensitive to even moderate concentrations of oxygen inhalation. Air has an approximate oxygen concentration of 21%. With the adjustable air inlet opening, current nebulizer designs produce a minimum oxygen concentration of about 28% in the resultant inhalation mixture, and more frequently produce a minimum oxygen concentration of 30%. Oxygen sensitive patients require an even lower minimum oxygen concentration in the inhalation mixture and, consequently, complicated air pressurizing and mixing apparatus are necessary in order to mix air with the pressurized oxygen before the carrier gas enters the nebulizer. This introduces unwanted complexity and cost to the patient undergoing treatment.
Another significant drawback to current nebulizer design is that the nebulizer is designed to attach to a carrier gas valve fixture on the wall in the patient's room thus making movement of the nebulizer set-up difficult and requiring that the patient be disconnected while being transported.
Another disadvantage with current nebulizer design is the relatively long delivery tube between the nebulizer at the fixed wall carrier gas valve and the patient. this results in low spots in the delivery tube where liquid condensation from the resultant carrier gas mixture accumulates. This condensation must be constantly monitored to prevent occlusion of the tubing resulting in possible loss of oxygen and aerosol flow to the patient. Moreover such condensation in the tubing results in the loss of medication and leads to excessive use of medication.
Accordingly there is a need for a portable nebulizer that entrains a greater amount of air into the inhalation mixture thus controllably allowing for decrease of the concentration of carrier gas and liquid medication and that reduces the amount of liquid waste and the need for constant monitoring of the nebulizer set-up.